Literature data indicate that sliding of vertebrae occurs on average in 10% of patients treated because of back pain. This pathology may cause a significant disability, both among the youth and adults. Surgical treatment of spondylolisthesis is provided when neurological symptoms and/or pain occur, or even increase, even though conservative treatment had been previously administered. Until now in medical practice, the most commonly used treatment has consisted in bringing the spine to spinal fixation by bone fusion on the sliding level. The spondylodesis itself is not always a sufficient means and does not bring positive results in the form of: restoration of proportions in the height of disc space, thereby reconstruction of the correct geometry, reduction of posture deformation, removal of pain discomfort, restoration of biomechanical balance. To achieve all of the above mentioned benefits, decompression of nerve structures and reposition of the displaced vertebra is essential.
Devices for spondylolisthesis reposition are known; most of all they are based on different kinds of pulling screws or special repositioning constructions, whose principal feature is a considerably large number of elements and surgical difficulties resulting from the complexity of the system removing this pathology.
Their application often involves extensive surgical actions, which significantly increase patient's burden and can lead to intra- and postoperative complications.
An implant, apparatus and a method for spondylolisthesis correction are known from the patent application WO 96/40016. The implant is in the form of one-element cage intended for blocking the dislocation of vertebrae, whereas the correction itself is performed with a specially designed apparatus introduced into the intervertebral space, including a longitudinal body composed of two elements, which by moving along each other, align the dislocated vertebrae. The disadvantage of this solution is the possibility of losing reposition during replacement of the corrective apparatus with the locking cage.
An apparatus and a method for the realignment and stabilization of adjacent vertebrae are known from the patent application US 2008/0319481. The implant has two halves which are interlocked so that they can slide horizontally with respect to each other. The movement of the implant halves and their respective positions are controlled by a screw set within the implant. The implant includes radial anchors which fit into alignment slots made in the misaligned vertebra. The screw set in the implant is used to advance the halves of the implant which in turn move the misaligned vertebrae back into correct positions. The solution provides for the correction of spondylolisthesis only by means of using the anterior surgical approach, which due to the possibility of disturbing important anatomic structures situated there, seriously hinders and sometimes prevents surgical activities and may pose considerable risk to the patient related; for example, to the prolonged duration of surgery. Another disadvantage of this solution is also the necessity of making an incision—with the use of a special instrument—for slots in the vertebral body for anchors. Yet another drawback is the complicated and difficult to control procedure of introducing the implant into the interbody space, requiring adapting its position to the slots prepared earlier. The screw gear employed allows movement only in one direction in the direction of the reposition of dislocated vertebrae. As there is no reverse mechanism, intraoperative correction and implant's removal are prevented, resulting in patient risk. Guiding employed in the form of a dove tail does not have any protection against locking of the shift due to the fact that the cooperating implant halves become distant from each other as a result of the elbowing action of the screw. Fixation of vertebrae position and locking of the implant itself require using additional means in the form of a nut and an additional fixing plate, and this increases the number of implant elements and moreover, irritates tissues.
An interbody spacer is known from the patent application US 2007/0123989 intended for surgical treatment of spondylolisthesis. The spacer is composed of two halves and a locking screw gear, installed using the anterior approach between two vertebrae and anchored in the vertebral body with bone screws in a variant connected with a reduction plate. In the disclosed embodiment, correction of spondylolisthesis is made by manipulating the adjusting mechanism in such a way that the first and the other half move along each other, thus aligning the vertebrae. The locking screw gear may have a central screw, which at rotation can move one of the halves forward or backward. In one embodiment of the screw gear, it can be a central rail allowing the movement of both halves forward and backward, and the mechanism can be secured by a lateral blockage. The adjusting mechanism employed does not offer the possibility of moving the halves along each other in opposite directions. Another disadvantage of this solution is the mechanism of anchoring the interbody spacer in the vertebral body, which does not provide a secure fixation during reposition and causes spacer's elements to project from vertebral margins after reduction of pathology, thus endangering biological structures situated in this area.